The present application claims priority to Japanese Patent Application No. 2001-239542 filed in the Japanese Patent Office on Aug. 7, 2001, the disclosure of which is incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a developing device that develops a latent image formed on a latent image carrier with a two-component developer, and more particularly, to an image forming apparatus such as a copying machine, a facsimile machine, a printer, or other similar image forming apparatus, including the developing device.
2. Discussion of the Background
In a developing device that develops a latent image formed on a latent image carrier with a two-component developer, a development mechanism typically includes a developer carrier (e.g., a development roller) and two developer conveying screws.
For example, Japanese Laid-open Patent Publication No. 4-191876 describes a developing device which includes a developer carrier that carries a developer while rotating, and two developer conveying screws arranged in parallel to each other and to a rotation center axis of the developer carrier at one side of the developer carrier in a direction orthogonal to the rotation center axis of the developer carrier. One of the two developer conveying screws is placed close to the developer carrier, and the other of the two is placed farther from the developer carrier. In this type of the developing device, a developer is circulated using the two developer conveying screws.
The two developer conveying screws perform mixture and conveyance of the developer in a superior manner in a horizontal direction (i.e., a longitudinal direction of the developer conveying screw). However, the mixture and conveyance of the developer in a direction orthogonal to the longitudinal direction of the developer conveying screw are not performed in a manner as well as that performed in the horizontal direction.
Accordingly, when a great amount of toner is supplied to a development mechanism, one of the two developer conveying screws placed closer to the developer carrier typically tends to cause a dirty background image due to insufficient charging of the toner supplied to the development mechanism and an uneven density in a form of a screw pitch (e.g., the formation of stripes of toner corresponding to threads of the screw).
Particularly, in a color image forming apparatus using the above-described developing device, the uneven density appears as an unevenness of color, thereby deteriorating image quality.
According to an aspect of the present invention, a developing device that develops a latent image carried on a latent image carrier with a two-component developer includes a developer carrier configured to carry a two-component developer while rotating, and a first developer conveying screw configured to convey the developer from a first end of the first developer conveying screw to a second end of the first developer conveying screw and to transfer the developer to the developer carrier. The first developer conveying screw is arranged about parallel to a rotation center axis of the developer carrier. The developing device further includes a second developer conveying screw configured to convey the developer from a first end of the second developer conveying screw to a second end of the second developer conveying screw and to convey the developer from the second end of the second developer conveying screw to the first end of the first developer conveying screw. The second developer conveying screw is arranged about parallel to the first developer conveying screw. A following relationship is satisfied:
T2xe2x89xa73T1, 
where T1 is a time for conveying the developer from the first to the second end of the second developer conveying screw, and T2 is a time for conveying the developer from the first to the second end of the first developer conveying screw.